ANISOTROPY OF OPTICAL ABSORPTION INTENSITY IN Tm3+ DOPED YVO4 CRYSTALS

Seven absorption group-bands (¹D₂, ¹G₄, ³F₂, ³F₃, ³H₄, ³H₅, ³F₄) of Tm³⁺ in YVO₄ single crystals have been observed in the orientation absorption spectra recorded in the spectral range from 200 to 4000 nm at 300K. The integrated absorption cross section for each group-band was accurately evaluated. On the assumption that the anisotropy of this uni-axial crystal is small, the Judd-Ofelt theory was extended for the calculation of 4f-4f transition intensities of Tm³⁺ in YVO₄. Two sets of phenomenological intensity parameters were derived from a least-squares-fit procedure. For c-axis cut sample we have Ω₂=10.18 (10^-20cm²), Ω₄=1.96 (10^-20cm²), Ω₆=0.75 (10^-20cm²).For a-axis cut sample we have Ω₂=8.20 (10^-20cm²), Ω₄=2.47 (10^-20cm²), Ω₆=0.91 (10^-20cm²). The anisotropy of the optical absorption intensities of Tm³⁺:YVO₄ was theoretically analyzed in detail.     

Tm,Ho双掺杂YVO4晶体中Tm对HO敏化发光现象

摘要报道了对Tm,Ho双掺YVO4晶体光谱性能的测量结果,包括用UV-365型分光光度计测出单掺TmYVO4及HoYVO4吸收谱以及双掺TmHoYVO4的吸收谱;用Ar离子激光器488nm,LD激光器激发测量样品荧光光谱;用J-O理论进行光谱参数计算及对能级结构进行分析;研究了在λ=805nm的激光二极管激发下Tm对Ho的敏化发光过程。发现与YAG,YLF为基质的Tm,Ho双掺材料相比,该材料中的Tm3+离子具有大而均匀的吸收宽度(～26nm),大的峰位吸收截面和积分吸收截面(～1.4×10-20cm2和274.5×10-20 cm),能量转换效率高(可达87％),且泵浦阈值低(～15mW)。表明了YVO4晶体中Tm能有效地敏化Ho,并产生2μm的发射。文中对发射强度与泵浦功率及Tm,Ho之间掺杂浓度的关系进行了初步的分析与讨论。光谱的观察结果表明在实现LD泵浦,全固体化,小型,高效的,2μm激光振荡的探索中,TmHoYVO4晶体将是一种很有实际应用潜力的材料。     

Analysis of the laser performance of Tm3+, Tb3+(Ho3+):YVO4 crystals at ～1.5μm wavelength

The absorption spectra of Tb,Tm:YVO_4 and Ho,Tm:YVO_4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, A_{i,j} and ω_{i,j}, and the cross-elaxation probability are calculated in virtue of Judd－Ofelt and Dexter theories. The fluorescence lifetime of Tm^{3+} in the Tb^{3+} (or Ho^{3+}) co-doped crystal is calculated. It indicates that the lifetime of initial level {}^3H_4 of the laser transition can be shorter than that of terminal level {}^3F_4 of the transition if the atomic percentage of Tb^{3+} (or Ho^{3+}) ions is bigger than about 1 at%: namely, by means of the co-doping Tb^{3+} (or Ho^{3+}) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P^{(4)}_{th} and the slope efficiency η^{(4)}_s of the four-energy-level system, we obtain the relationship of threshold power P^{(4)}_{th} to the concentration of Tm^{3+} ions and discuss the effect of Tb^{3+} (or Ho^{3+}) ion concentration on the laser threshold power P^{(4)}_{th} around 1.5μm wavelength. The result shows that Tb,Tm:YVO_4 crystal is a better choice to make the laser at ～1.5μm wavelength than Ho,Tm:YVO_4 crystal. We give the appropriate composition of (1－2) at% Tb, (1－2) at% Tm:YVO_4, just for reference.     

YNbO4：Tm3+/Yb3+上转换发光特性研究

按照50Nb₂O₅-（46-x）Y₂O₃-4Yb₂O₃-xTm₂O₃（x=0.1,0.2,0.5,1,2）的配比方式,采用高温固相法制备出了掺杂Tm³⁺/Yb³⁺的YNbO₄晶体粉末。在980 nm红外光激发下,观测到波长为478,645,707 nm的上转换荧光,分别对应于Tm³⁺离子的¹G₄→³H₆、¹G₄→³F₄、³F₃→³H₆能级跃迁过程。利用上转换发射功率与980 nm激光器工作电流关系估算出跃迁过程吸收光子数目为2.72,2.69,2.01,从而确定出前两者为三光子吸收过程,最后一个对应于双光子吸收过程。运用Judd-Ofelt理论研究样品光谱特性,根据样品的吸收谱得到样品的谱线强度参数Ω_t（t=2,4,6）,进而得出理论振子强度及实验振子强度,二者均方根偏差δ_rms=1.299×10^-7。计算了Tm³⁺离子向下能级跃迁的跃迁几率、跃迁分支比等参数。最后得出结论：（1）³F₄能级寿命较长,适合作为上转换中间能级;（2）³H₅能级寿命较长,且³H₅→³H₆跃迁分支比（96.46%）接近100%,可用于产生1 216 nm激光。     

SPECTROSCOPIC INVESTIGATION ON THE PROPERTIES OF VISIBLE AND NEAR INFRARED EMISSIONS IN Tm3+, Ho3+ Co-DOPED YVO4 CRYSTALS

With the help of absorption and fluorescence spectra, the spectroscopic properties of Tm³⁺, Ho³⁺:YVO₄ crystals have been investigated under different dopant concentrations. The absorption results show that the maximum absorption in the spectral range of currently available powerful laser diodes (LD) is at 796 nm, corresponding to the transition ³H₆→³H₄ of Tm³⁺ in the crystals. Upon the excitation with a LD at 808 nm, we have detected ten fluorescence bands in the spectral range spanning from visible to infrared. In visible region 4 upconversion bands have been observed centered at 475, 547, 660, and 701 nm. Discussions of the energy transfer processes suggest that cross relaxations and excited absorptions with the involvement of Tm^{3+ 3}F₄, ³H₅ and Ho^{3+ 7}I₅ states are responsible for the four upconversion emissions. Comprising the relative integrated intersities of 2 μm (Ho³⁺: ⁵I₇→⁵I₈) and 1.8 μm (Tm³⁺: ³F_4→³H₆) bands we have observed an efficient energy transfer from Tm³⁺ (³F₄) to Ho³⁺ (⁵I₇). Examination of the ratios of the intensity of 2 μm band to that of 1.8 μm band as a function of the ratios of Tm³⁺ concentration (c_Tm) to Ho³⁺ concentration (c_Ho) indicates that small concentration ratios (c_Tm/c_Ho) lead to high efficient energy transfers of Tm³⁺(³F₄)→Ho³⁺(⁵I₇).     

小尺寸NaLuF4:Yb3+/Tm3+纳米晶的生长及上转换发光

为了详细地探究NaLuF₄纳米晶的生长过程,利用自主研发的可以精确控制实验参数的自动纳米合成仪制备了不同系列的NaLuF₄：Yb³⁺/Tm³⁺纳米材料。对不同反应温度下（285,295,305℃）制备的样品进行物相分析,发现随着反应时间的增加,NaLuF₄纳米晶均遵循相似的生长规律,即α-相→α-相+β-相→均匀的β-相→聚集的β-相。在不同温度下,均有一个时间段可以获得小尺寸（小于50 nm）、单分散、粒径分布窄的纯β-NaLuF₄纳米晶。另外,测试了不同温度下制备的β-NaLuF₄：Yb³⁺/Tm³⁺纳米材料的上转换发射光谱,结果表明随着反应温度的升高,样品的发光先增强后减弱。出现这种光谱规律可能是受晶体尺寸和结晶性两方面因素的影响。此外,样品在紫外区的高阶多光子发光很强。例如,361 nm发射峰强度大约是800 nm发射峰强度的2倍。     

Charge transfer excitation of the Nd3+, Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ emission in CaGa2S4

The excitation spectra of the Nd³⁺, Sm³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Tm³⁺ emission in the sodium-compensated CaGa₂S₄ host lattice, a sulfide with wide band gap, contain an intense band below the absorption edge. Comparison of the energy of its maximum with thermodynamic data and correlations to Jørgensen's refined spin-pairing theory predictions allow one to ascribe this band to a charge transfer transition ending onto 4f orbitals. The irregular variation within the rare earth series contrasts with the monotonic variation of the absorption edge in stoichiometric rare earth sulfides (e.g. NaLnS₂), associated with interband transitions.     

氟锆酸盐玻璃中Tm^3＋和（Tm^3＋＋Ho^3＋）离子的光谱研究

给出氟锆酸（ＺＢＬＡＮ）玻璃中＾Ｔｍ＾３＋和Ｈｏ＾３＋离子的Ｑｔ参量，并与氧化物玻璃中Ｔｍ＾３＋和Ｈｏ＾３＋的Ｑｔ参量进行了比较，用３７５ｎｍ和４６８ｎｍ波长激发单掺ＺＢＬＡＮ中Ｔｍ＾３＋离子，获得来自Ｄ，２，＾３Ｈ４，Ｇ４能级不同发射波长的发光强度随掺杂浓度的变化，而用小于１μｍ的激发波长激发发单掺Ｔｍ＾３＋或Ｈｏ＾３＋样品，获得近红外区发射光谱。文中给出掺杂浓度对于Ｔｍ＾３＋和Ｈｏ＾＋近红外区     

近红外光诱导下NaYbF4:Tm3+,Eu3+ 体系中Eu3+的上转换发光

利用水热法制备得到NaYbF₄:0.01%Tm³⁺,20%Eu³⁺上转换材料,利用X射线衍射分析、扫描电子显微镜及光谱测试技术分别对其进行了结构、形貌以及光谱性质的表征。在980 nm近红外激光激发下,得到了Eu³⁺的可见到紫外范围的上转换荧光发射。分析表明:共掺杂NaYbF₄纳米材料中Tm³⁺到Eu³⁺离子的能量传递对布居Eu³⁺离子的激发态能级,获得Eu³⁺的上转换发光起着至关重要的作用。另外,在实验中首次获得了Eu³⁺对应于³P₀→⁷F_j (j=0,1,2)能级跃迁的上转换光发射。     

Spectroscopic investigation of a new crystal： Nd^3＋,Yb^3＋：YVO4

The absorption and emission spectra of the YVO4 single crystal co-doped with 1 at.% Nd^3＋ and 1 at.% Yb^3＋ are investigated. The efficient Nd^3＋ → Yb^3＋ energy transfer and the back transfer （Yb^3＋ → Nd^3＋） are observed at room temperature. The fluorescence lifetime of the 4F3/2 level of Nd^3＋ in Nd,Yb：YVO4 is measured under 808 nm laser light excitation. The efficiency of Nd^3＋ → Yb^3＋ energy transfer in YVO4 is determined to be about 34%.     

Tm3+,Yb3+共掺钨酸钙多晶材料的上转换发光及荧光温度特性

采用高温固相法制备了Tm³⁺,Yb³共掺CaWO₄多晶材料. 980 nm二极管激光器激发下,在可见区获得了¹G₄→³H₆,¹G₄→³H₄,³H₂,³H₃→³H₆ 跃迁产生的上转换荧光. 讨论了Yb³⁺ 离子浓度的变化对Tm³⁺ 的上转换发光强度的影响,同时根据荧光强度比的方法研究了689 和705 nm 红色上转换荧光在313–773 K 范围内的温度特性. 结果表明：基于Tm³⁺,Yb³⁺ 共掺CaWO₄ 多晶材料的红色上转换荧光可以实现温度监测,其测温的最大灵敏度值为5.7×10^-4 K^-1,相应的测量温度为458 K. 关键词： 上转换发光 3+')" href="#">Tm³⁺ 钨酸钙 荧光温度传感     

UPCONVERSION FLUORESCENCE DYNAMICS OF Tm3+ IONS IN LiYF4 CRYSTAL

According to Judd-Ofelt parameter calculation and energy transfer theory, the cross-relaxation process of the Tm³⁺ ions is investigated. A four-level system of coupled rate equations is established to study the fluorescence dynamics of Tm³⁺ in LiYF₄ crystal. Attentions are focused on the upconversion luminescence ¹G₄→³H₆ (483.0 nm) in Tm³⁺:LiYF₄. The relationship between the avalanche properties (critical pump rate, fluorescence intensity and buildup time) originated by resonant excited state absorption and the doped Tm³⁺ concentration is discussed, and some useful conclusions are drawn.     

近红外到近红外Mn2+掺杂NaYF4:Yb3+/Tm3+纳米粒子的制备及其生物成像

在反应温度为200℃、反应时间为8 h的温和条件下,采用水热法合成了近红外到近红外的Mn²⁺掺杂NaYF₄:Yb³⁺/Tm³⁺上转换荧光纳米粒子,再以两亲性聚合物C₁₈PMH-mPEG作为亲水性配体修饰到上转换荧光纳米粒子表面,得到具有水溶性的上转换荧光纳米粒子。然后在980 nm近红外光源激发下,测量了上转换荧光纳米粒子的荧光发射光谱,在（800±10） nm附近,观察到了较强的单近红外光发射（³H₄→³H₆）。对样品进行细胞毒性实验,结果表明制得的水溶性Mn²⁺掺杂NaYF₄:Yb³⁺/Tm³⁺纳米粒子具有良好的生物相容性。并进一步在小鼠体内进行了近红外成像,表明其在生物成像领域将会具有一定的应用前景。     

Yb~(3+)/Tm~(3+)共掺杂Sb_2O_4荧光粉的制备及上转换发光性质研究

高温固相法制备了Yb3+/Tm3+共掺的Sb2O4发光粉体,研究了其上转换发光性质。在980nm半导体激光器的激发下,样品发射较强的近红外(800nm)和较弱的蓝色(480nm)及红色(680nm)上转换发光。粉末样品中稀土Yb3+及Tm3+浓度对上转换发光性质具有显著的影响,随着Yb3+或Tm3+浓度的增加,上转换发光增强;Tm3+掺杂浓度达0.8%时其上转换发光强度达到最大,之后上转换发光随Tm3+浓度的增加而减弱,这是由于浓度猝灭引起的。探讨了粉末样品的上转换发光机理,在980nm激发下Tm3+的蓝光和近红外上转换发光均属于二光子的上转换发光过程。     

钬铥双掺钨酸镱钾激光晶体光谱参数计算

采用顶部籽晶提拉法（TSSG）生长了钬铥双掺钨酸镱钾（KHo_0.04Tm_0.06Yb_0.9（WO₄）₂）激光晶体。测试了该晶体的吸收及荧光光谱,计算了其光谱参数。实验结果表明：该晶体在890~1 000 nm范围吸收带较宽,半峰宽为90 nm,计算了主峰1 000 nm处吸收截面为16.92×10^-20 cm²;Tm³⁺在1 690~1 812 nm范围存在较宽的吸收带,半峰宽为118 nm,易于实现Yb→Ho、Yb→Tm、Tm→Ho的能量传递。根据Judd-Ofelt理论,计算了该晶体的光谱强度参数。根据Tm³⁺、Ho³⁺、Yb³⁺离子能级图,讨论了产生1 750~2 200 nm荧光发射的3种能量传递方式。最后计算了主峰2 030 nm处受激发射截面为3.47×10^-20 cm²,表明该晶体可作为2 μm波段优异的激光增益介质。     

端抽运Yb3+:YVO4激光准三能级理论模型研究

立足于Yb离子能级结构、谐振腔增益损耗和布居数分配情况, 利用爱因斯坦辐射理论和速率方程理论, 建立了适合Yb³⁺离子激光的准三能级理论模型. 该模型引入有效腔长增益贡献因子对腔内光强进行了从头计算, 获得了阈值方程. 利用此模型与Yb激光的实验结果相比较, 发现有效腔长对增益的贡献可以改变腔内损耗和粒子数反转的概率, 也继而影响激光阈值和输出功率效率. 应用于LD端抽运Yb³⁺:YVO₄激光实验中, 在971 nm LD抽运, 有效晶体长度 L=1 mm, 输出镜透过率对激光波长1016 nm为1%条件下, 获得阈值为1.1 W; 有效晶体长度L=2 mm, 输出镜透过率为10%条件下, 阈值获得为3.9 W. 关键词： 3+:YVO₄')" href="#">Yb³⁺:YVO₄ 准三能级模型 有效腔长增益贡献因子     

FLUORESCENCE MECHANISMS OF Tm3+- AND Yb3+/Tm3+ DOPED AlF3-BASED FLUORIDE GLASS

A complete set of spectroscopic parameters, including Judd-Ofelt parameters, radiative transition probabilities, radiative lifetime, branching ratios and integrated absorption cross section, have been calculated for Tm³⁺- doped fluoroaluminate (AYF) glass, based on the measured absorption spectra. The mechanism of Tm³⁺→Tm³⁺ and Yb³⁺\Leftrightarrow Tm³⁺ energy transfers and fluorescence properties have been investigated in both Tm³⁺ single-doped and Yb³⁺/Tm³⁺ double-doped AYF glasses. The cross-relaxation process, ³F₄+³H₆→2³H₄, is proved, which makes the optimum Tm³⁺ concentration of 1.77μm fluorescence (³H₄→³H₆) much higher than 1.45μm fluorescence (³F₄→³3H₄) in Tm³⁺:AYF glasses. In Yb³⁺/Tm³⁺:AYF glasses, a stronger concentration quenching is found for the 476nm emission than that for the 797nm emission, and is discussed under the 970nm-excitation.     

Tm3+/Yb3 :LiYF4单晶的高效近红外量子剪裁及其在光伏电池中的应用

采用改进的坩埚下降法成功地生长了Tm/Yb共掺氟化钇锂单晶. 该单晶体具有每吸收一个蓝色光子并能发射出2个1000 nm近红外光子的下转换发光效应. 测定了样品的激发光谱、发射光谱和荧光衰减曲线. 在465 nm蓝光激发下观察到由Yb³⁺：²F_5/2→²F_7/2能级跃迁所致的960～1050 nm 波段的发射带,此发光带源于Tm³ 对Yb³ 离子的能量下转换过程. 应用Inokuti-Hirayama模型,研究了晶体的能量转换过程,结果表明Tm³ 向Yb³ 的能量传递是一个电偶极子相互作用机制过程. 当Tm³ 与Yb³ 离子的掺杂浓度为0.49mol%与5.99mol%时,单晶的量子剪裁效率达到最大值167.5%.     

Tm3+/Ho3+共掺碲酸盐微结构光纤激光器

用棒管法拉制了Tm³⁺/Ho³⁺掺杂的碲酸盐微结构光纤,并获得了2 μm的激光输出。以1 560 nm的Er³⁺掺杂石英光纤激光器作为泵浦源,在22 cm长的微结构光纤中,得到了最大功率为8.34 mW、波长为2 065 nm的连续激光输出,泵浦光功率为507 mW,斜率效率为2.97%。研究结果表明,Tm³⁺/Ho³⁺共掺碲酸盐微结构光纤是一种用于研制2 μm激光器的理想材料。     

Tm3+/Yb3+/Er3+共掺氟氧硅酸盐玻璃的上转换发光特性

利用熔融法制备了Tm3+/Yb3+/Er3+共掺氟氧硅酸盐玻璃.在980nm LD激发下,研究了Tm3+离子和Er3+离子之间的能量传递和Tm3+离子的上转换荧光,分析了Tm3+离子的上转换机理,发现蓝色上转换荧光是三光子过程对应于1 G4→3 H6的跃迁,而红色上转换荧光是双光子过程对应于1 G4→3 F4的跃迁.比较不同掺杂摩尔分数的样品的荧光强度,发现Tm3+离子的最佳掺杂摩尔分数为0.2%.